In the manufacture of semiconductor circuits resistor elements are commonly created using thin film resistors (“TFR”). Thin film resistors are usually made of a metal that is combined with another material to mitigate the resistance of the metal and make the thin film resistor material have a high resistance. One typical example of a thin film resistor material is silicon carbide chrome (“SiCCr”). Another typical example is tantalum nitride (“TaN”).
Because a high resistance per unit area is generally desired for a thin film resistor, the thickness of a thin film resistor is usually very thin. For example, a thin film resistor may have a thickness from seventy five Ångstroms (75 Å) to one hundred Ångstroms (100 Å). This thickness range may also be expressed as a range from seven and one half nanometers (7.5 mm) to ten nanometers (10.0 nm).
The requirement that a thin film resistor be very thin presents manufacturing problems. During the manufacturing process it may be very difficult to accurately control the thickness of a thin film resistor. The deposition rate of a thin film resistor is relatively high. Any slight variation in the deposition rate will change the thickness of the thin film resistor and affect the value of the resistance of the thin film resistor. Variation in the resistance of the thin film resistors in a semiconductor circuit causes inferior integrated circuit device performance, leading to low yields, increased scrap, and lost market opportunities.
Therefore, it would be desirable to have a method to adjust the value of resistance of a thin film resistor after the thin film resistor has been manufactured. One prior art method for adjusting the value of resistance of a thin film resistor employs thermal cycles. However, the use of thermal cycles is not always practical. One problem is that a thermal cycle is not self limiting. It is possible that the thermal cycle method may introduce more variation in the resistance of a thin film resistor than it eliminates.
Therefore, there is a need in the art for an efficient system and method for adjusting a value of resistance of a thin film resistor after the thin film resistor has been deposited in a semiconductor manufacturing process.